Bandwidth constrained or narrowly filtered communication systems are defined in U.S. Pat. No. 8,155,530 to Alic et al., incorporated herein by this reference.
Ability to reliably transmit a high quantity of information over a given bandwidth is the single most important aim of communication systems. In designing the communication systems, predominantly modulation formats without memory are used. As is well known, these systems, often based on quadrature amplitude modulation (QAM) cannot reach theoretical bounds of spectral efficiency. On the other hand, when mated with very sophisticated encoding schemes that jointly optimize the modulation and error control coding (ECC), communication systems without memory are known to perform closer to the theoretical bounds. The error-control codes append redundant information bits, or symbols, so as to achieve resilience and/or an improved performance in the presence of hindrances in the process of the information transfer, such as noise and distortions. Specifically, it has recently been demonstrated that utilization of more than one error control code, in the encoding process, in a construction best described as multiple level information protection, can yield an improved performance, especially if mated with the so called iterative decoding, in which the reliability estimates on the received information symbols are exchanged between the constituent codes' decoders multiple times, with an improved estimate on the information symbols being obtained with each additional iteration. In particular, in the context of iterative decoding, it is often said, owing to the particular encoding implementation that the constituent codes are concatenated. In particular, the process of concatenation is achieved by constructs called interleavers that in effect permute the order of either the input information symbol prior to encoding, or permute the order of encoded information symbols. Conversely, the action of restoring the input information order is achieved by de-interleavers at the receiving end. The process of iterative decoding encompasses the interleaving and the de-interleaving process in that passing of the codewords between multiple constituent decoders is assumed to include the permutation of the relevant information symbols so as to be corresponding to the pertinent constituent codes.
The key aspect of the present invention is that if bandwidth constriction (or introducing memory into the communication system by design) is used appropriately in conjunction with error control coding—a novel, previously unsuspected quality is attained in that the described simple arrangement can operate even closer to the theoretical bounds than the systems mentioned above. Thus, the main characteristic of the present invention is its ability to provide outstanding performance and capacity, based on a simpler design than existing communication systems' concepts. On the other hand, bandwidth constrained communication systems rely on equalization to mitigate the effect of bandwidth limitation. In particular, the systems with high spectral efficiency, or equivalently—a considerable amount of bandwidth limitation, can be affected by significant extension of the channel response duration, thus requiring long, and/or complex equalization structures to appropriately handle the effects of the induced intersymbol interference. Complex equalizers not only contribute to a significant complexity increase and difficult practical realization, but also increase the overall system power consumption. Consequently, the existing solutions fail to meet the industry needs since, for high spectral efficiencies, they result in both an inferior performance, as well as in overly intricate, and thus highly power hungry solutions.
Currently there are a number of solutions for improving capacity (i.e. the amount of information reliably transmittable over a given bandwidth). Some of these solutions attempt to utilize modulation formats without memory, such as QAM, mentioned above, but these solutions fail to meet the needs of the industry because QAMs cannot operate close enough to the theoretical bounds. Other solutions attempt to use specific (i.e. redundant) encoding for information in order to improve performance, but these solutions are similarly unable to meet the needs of the industry because they still cannot provide adequate performance. Still other solutions seek to jointly optimize modulation and error control coding (ECC) by means of e.g., trellis coded modulation, but these solutions also fail to meet some specific industry needs because of the associated complexity of that solution.
The narrowly filtered, or bandwidth constrained systems with high spectral efficiency necessarily need to rely on equalization for information retrieval from severely distorted information-bearing waveforms at the receiving end of the link. In addition there exist a number of solutions for equalization in digital communication systems affected by intersymbol interference. Some of these solutions attempt to mitigate the effects of intersymbol interference by equalization that corresponds to the full extent of the channel response duration (in terms of the number of symbol slots affected by intersymbol interference), but these solutions fail to meet the needs of the industry because a direct equalization often yields complex equalization structures. Other solutions attempt to use simpler equalization structures, but these solutions are similarly unable to meet the needs of the industry because they do not provide satisfactory performance.
The overall performance and the underlying complexity of the equalizer used in communication systems represent critical concerns in their practical realization, and are of particular importance for high speed systems. The said properties translate to both higher reliability and/or capacity in communication systems, as well as a lower receiver and system overall power dissipation and an easier practical implementation. Consequently, there currently exists a clear need in the industry for means of improving the performance and capacity of communication systems, in addition to reducing the complexity of the underlying digital receivers.
In that respect, it would be desirable to have a composition that can have a simpler design than the existing ones which/that can be used to provide performance close to the theoretical bounds. Still further, it would be desirable to have a compound that can be used as an add-on solution to the existing systems and provide them with a superior performance.
In that respect, it would be desirable to have a composition that avails an improved performance and/or capacity which has a limited complexity. It would be desirable to have a composition that can have a simpler design than the existing ones which/that can be used to provide performance close to the theoretical bounds. Furthermore, it would also be desirable to have a composition whose practical implementation is straightforward. Still further, it would be desirable to have a compound that can be used as an add-on solution to the existing systems and provide them with a superior performance. Furthermore, it would be desirable to have a compound that introduces a low latency in processing. In summary, there currently exists a need in the industry for a composition that is instrumental in providing an improved performance while forgoing a complex equalization structure and is, yet, capable of handling large amounts of intersymbol interference with limited penalties.